Return to story

Equinox marks time of change

September 6, 2007 12:35 am

I AM ALWAYS amazed about how astronomical objects directly influence our lives in ways we don't always realize or appreciate.

September provides examples of such things. The sun's lower angle in the sky signals the last of summer in the Fredericksburg area, and the moon plays a special role at the end of the month.

Let's talk first about the sun. Its influence will be felt as the autumnal equinox begins Sept. 23. The autumnal equinox is one of the two days of the year (the other being the vernal equinox in March) when the sun rises directly in the east and sets directly in the west.

During the autumnal equinox, day and night are equal in duration, though our days will continue to shorten until the winter solstice occurs in late December.

Autumn's shorter days lead to less light, but the moon will help remedy that situation late this month.

Traditionally, the full moon closest to the autumnal equinox is called the Harvest Moon, and there is a good reason for this catchy name. Normally, the full moon rises about 50 minutes later each night, but for a few nights during this time of year, it rises only 30 minutes or so later each night. This shorter interval of darkness between sunset and moonrise allows farmers to harvest crops in the evenings after sunset. The Harvest Moon occurs on the 26th this month.

Our ancestors realized the importance of recognizing the change of seasons. Their lives depended on knowing when to plant and harvest crops, hunt animals, and seek shelter from the changing weather. They built fairly accurate structures of stone to measure the seasons and the passage of time. The most well-known of these ancient calendars is Stonehenge in England, but others were built also by the Mayans in Mexico and the American Indians in Wyoming to name a few.

While our ancestors' routines changed with the dwindling daylight between autumn and winter, modern conveniences have masked and consequently lessened the impact we feel today. But make no mistake; our lives will always be intertwined with the cycles of darkness and light regardless of technology's facade.

This month, NASA is scheduled to launch the Dawn spacecraft on a 4-billion-mile, eight-year mission to the asteroid belt.

The Dawn mission will study two massive asteroids, Ceres and Vesta, to help scientists understand how the solar system formed.

The Dawn spacecraft will use an ion-propulsion system to enable the spacecraft to meet its challenging goal of orbiting each of the two asteroids, several years apart.

Ion propulsion may sound like the stuff of science fiction, but the Dawn team has made it a reality. Learn more about the mission at dawn.jpl.nasa.gov.

With the somewhat cooler weather, venturing outdoors to stargaze should be very enjoyable this month.

For early weekend risers on Sept. 8 and 9, the thin crescent moon will be near bright Venus about an hour before sunrise in the early morning sky. The pair will be close together, but not as close as they were earlier this year in May's evening sky. My photo shows the beautiful duo gracing the skies of Stafford on May 19.

For evening viewers on the 17th through the 19th, the moon will glide by Jupiter in the area's southwestern sky about an hour after sunset. Jupiter will be the bright, white-colored point of light above the moon on the 17th and to the moon's right by the 19th.

The Rappahannock Astronomy Club hosts monthly star parties where you can view the moon, planets, and other celestial objects through amateur telescopes. For more information, visit raclub.org on the Web.